Direct view imaging tube incorporating velocity selection and a reverse biased diode sensing layer

ABSTRACT

A direct view imaging tube which incorporates a reversed biased diode array sensing structure for sensing input radiation to modulate a velocity selection type image section.

United States Patent [1 1 McNally DIRECT VIEW IMAGING TUBE INCORPORATINGVELOCITY SELECTION AND A REVERSE BIASED DIODE SENSING LAYER [75]Inventor:

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: June 21, 1971 [21] Appl. N0.: 155,080

Frank X. McNally, Baltimore, Md.

[52] U.S.Cl ..3l5/10,315/11,315/21, 313/65 R [51] Int. Cl. H0lj 31/26[58] Field of Search 315/10 R, 10 X, 11R, 315/11 X; 313/65, 66, 67

[56] References Cited UNITED STATES PATENTS 3,560,756 2/1971 Labuda313/66 3,435,234 3/1969 Demon et a1. 313/66 X Nov. 27, 1973 2,903,5968/1959 Reed 313/67 X 2,888,513 5/1959 Melamed et a1. 313/67 X 2,550,3164/1951 Wilder 313/67 2,945,973 7/1960 Anderson 313/66 X 2,898,499 8/1959Sternglass et a1 313/67 X 3,201,630 8/1965 Orthuber et a1. 313/67 X3,423,623 1/1969 Wendland 315/10 3,646,390 2/1972 Silver 315/113,541,383 11/1970 Pruett et a1. 315/10 Primary ExaminerCar1 D. QuarforthAssistant Examiner-P. A. Nelson Attorney-F. H. Henson et a1.

[57] ABSTRACT A direct view imaging tube which incorporates a reversedbiased diode array sensing structure for sensing input radiation tomodulate a velocity selection type image section.

5 Claims, 2 Drawing Figures DIRECT VIEW IMAGING TUBE INCORPORATINGVELOCITY SELECTION AND A REVERSE BIASED DIODE SENSING LAYER BACKGROUNDOF THE INVENTION This invention relates to a light sensitive direct viewimaging device and more particularly to that utilizing a reverse biaseddiode type sensing structure associated with a velocity selection typetube.

Television camera tubes utilizing semiconductor diode array targetsensing structures and then scanned by an electron beam for deriving asignal representative of input radiation directed onto the target arewell known in the art. Such structures are generally discussed in US.Pat. No. 3,419,746 issued Dec. 31, 1968 to Crowell et al. Utilization ofan electron beam for reading the silicon type diode array target isfound to exhibit some problems. More particularly, the areas of thetarget between the p-n junctions may charge up in that an insulatingcoating is normally provided on this intervening area. Some of thearrangements proposed in the art to solve this problem result in lateralleakage at the surface which is difficult to reduce when utilizing thebeam reading method. Elimination of the electron beam readout wouldobviously solve such a problem.

It is also obvious that the utilization of a pick-up tube in combinationwith a display or monitor device and associated circuitry is much morecomplicated than a simple direct view imaging tube. The speed ofresponse of a photoconductor may be about 0.03 seconds while that of adiode is about seconds.

SUMMARY OF THE INVENTION A direct view imaging tube which incorporates areversed biased diode array sensing structure associated with a velocityselection tube so that the advantages of the semi-conductor wafer p-njunction technology and radiation detecting capability can be combinedwith the contrast enhancement of the velocity selector tube. A preferredembodiment of the invention incorporates a velocity selection type imagetube including a photoemissive mosaic surface within the interior of thetube and provided on an input window. Electrically conductive membersextend through the input window with the inner end of the conductivemember in electrical contact with a photoelectric island. The exteriorends of these conductive members or pins are in electrical contact witha reverse bias silicon diode. The diodes are formed by utilizing asilicon wafer of p-type conductivity, providing an n-type dopant on theouter surface of these conductive pins and then pressing the ptypesilicon wafer against these conductive pins and by heat treatmentforming a p-n junction within the silicon wafer. The silicon waferprovides the sensing portion of the device and also controls theemission from the photoemissive surface within the tube corresponding tothe input radiation directed onto the silicon wafer.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of theinvention, reference may be had to the preferred embodiments, exemplaryof the invention, shown in the accompanying drawings, in which:

FIG. 1 is a schematic illustration of a direct view imaging tube inaccordance with the teachings of this invention; and

FIG. 2 is an enlarged sectional view of a part of the apparatus shown inFIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a directview imaging device comprising an evacuated envelope 10. The envelope 10consists of a tubular body portion 12, an output end wall 14 and aninput end wall 16. The input end wall 16 comprises a plurality ofelectrically conductive members 18 which are embedded in an insulatingmatrix 20 and extend throughthe matrix 20; The diameter of the wires 18may be about (12 X l0cm) and the wires 18 may be spaced at a distance ofabout (50 X 10"cm) from each other. The wires 18 may be of a suitablematerial such as tungsten. The insulating matrix 20 may be of anysuitable material such as glass. It is also possible to utilize a moreconductive materialfor the matrix 20 and provide insulating sleevesaround the wires 18. The input end wall 16 is vacuum tight throughout.

A photoemissive mosaic coating 22 is provided on the inner surface ofthe end plate l6'and is positioned as a mosaic pattern so as to providea photoemissive element 24 in electrical contact with each of the wires18 extending through the end wall 16. A suitable photoemissive materialis cesium antimonide. Spaced by a small distance such as A to l inchdepending upon the electron optics, from the mosaic coating 22 is afirst electrical conductive grid 26 and spaced by a similar distancefrom the grid 26 is a second electrical conductive grid 28. The grids 26and 28 may have a mesh spacing of 500 to 750 spaces/inch and of asuitable material such as copper plus iron plating. An output screen 30is provided on the output end wall 14 and may be of an electronbombardment sensitive material such as phosphor which emits light inresponse to electron excitation. An electrically conductive backing 32of a material such as aluminum may be provided over the phosphor layer30. The electrically conductive layer 32 is connected by means of a lead34 to the positive terminal of a DC potential source 36. The grid 26 isconnected by a suitable lead 38 to the positive terminal of a DCpotential source 40 with the negative terminal of the source 40connected to the negative terminal of the potential source 36. The grid28 is connected by means of a lead 42 to the negative terminal of a DCpotential source 44 with the positive terminal of the source 44connected to the negative terminal of the potential source 36. Thepotential of the source 36 may be about 5 to 8 volts. The potential ofthe source 40 may be about 10 volts and the source 44 may be about 8volts.

A sensing member 50 is provided external of the vacuum envelope l0 andin front of the input window 16. The sensing member 50 is comprised of awafer 52 of a suitable semiconducting material such as silicon. Thewafer 52 may have a thickness of 20 X 10" cm to X 10 cm and of amaterial such as silicon with a resistance of about 10 ohm-centimeter.The outer surface of the wafer 52 may have a p+ region 54 for making anohmic contact to the p-type silicon wafer, and reducing radiationreflection. A lead 56 connects the p+ region 54 to the negative terminalof the potential source 36. The inner surface of the wafer 52 is securedto the lead members 18 extending from the end wall 16 'to provide an n+region 17 about each contact. This structure may be fabricated byelectroplating the extension of the leads 18 from the front of the endwall 16 with a material suitable for doping the p-type silicon ton-type. One suitable material is arsenic which may be electroplated ontothe electrical conductive lead 18. The wafer 50 is then placed inphysical contact with the electroplated leads l8 and then region 17 maybe formed by passing current through the lead 18 or by heating theassembly. A p-n junction 19 is formed between each of the regions 17 andthe wafer 52. The sensing member 50 may be attached to the end wall 16either prior to assembling the end wall 16 to the envelope or if desiredthe sensing member 50 could be secured thereto after the envelope 10 hadbeen evacuated and processed.

In the operation of the device, input radiations from a scene 70 aredirected through a suitable focussing system 72 onto the sensing member50. An external light source 74 directs radiation of uniform intensityover the mosaic layer 22 which causes emission of photoelectronsresulting in a positive potential being applied to the n-type elements17 with respect to the negative potential applied by the source 36 tothe p-type region 52 of the target 50 thereby establishing a reversebias across each of the p-n junctions 19. Without incident radiation onthe sensing layer 50, electrons emitted by the photoemitting layer 22will be accelerated through the accelerating grid 26, but due to therelatively high positive potential on the mosaic photoemissive surface22 these electrons will not be able to overcome the negative retardingpotential applied to the grid 28 and, therefore, no electrons willbombard the output screen 30. When radiation from the scene 72 isdirected onto the sensing layer 50 electron-hole pairs are generatedwithin the p-type region 52 of the sensing layer 50. The holes are drawnto the negative potential while the minority carriers, namely electrons,pass through the depletion region of the junction 19 and enter then-type region 17. This resultant charge flow passes along the lead 18 tothe photoemissive surface 22 and makes the potential more negative atthe photoemissive surface 22. This in effect then adds energy to thephotoelectron emitted by the photoemissive surface 22 and thephotoelectrons are able to overcome the retarding potential of the grid28 and are accelerated by the potential from the source 36. Electronspassing through the grid 28 are focussed by suitable focussing meanssuch as a coil 78 onto the output screen 30. Thus an image is formed onthe output screen 30 corresponding to the spatial distribution of theradiation image directed onto the sensing layer 50.

It is obvious that certain other applications are possible. A sensinglayer may be utilized which is sensitive to electron input. Such asensing layer would be provided within the envelope and a photoemissiveinput would convert the input radiation to electrons and then direct theelectron directed onto the sensing layer sensitive to electronimpingement. It is also possible to utilize a radiation conversion layersuch as a phosphor which emits radiation of a different wavelength thanthose received to which the sensing layer 50 would be sensitive. It isalso possible that the sensing layer 50 could be provided within theenvelope and simply evaporate the photoemissive material directly ontothe n-type region 17.

I claim as my invention:

1. An image device comprising an input sensing member comprised of awafer of semiconductive material of a first type of conductivity havingan input and an output surface, a plurality of regions of semiconductivematerial of a second type of conductivity of opposite type conductivityto said first type on the output surface of said wafer and extendinginto said wafer a discrete distance and forming a plurality ofjunctions, said input sensing member exhibiting'the property ofgeneration of electron-hole pairs in response to incident radiationdirected onto said input surface, means for reverse biasing saidjunction comprising a photoemissive element and means for electricallyconnecting the photoemissive element with each of said regions and meansfor illuminating said photoemissive elements, an output screenassociated with said photoemissive elements to generate a light image inresponse to the photoelectrons emitted from said photoemissive elementsstriking said output screen, a first grid positioned adjacent to saidphoto-emissive elements for accelerating the photo-electrons emittedfrom said photoemissive elements and a second grid positioned betweensaid accelerating grid and said output screen for velocity selection ofthe photoelectrons emitted from said photoemissive elements and passingthrough said accelerator grid, said sensing member responsive to saidinput radiations to modify the potential of said photoemissive elements.

2. The device of claim 1 in which said means for electricallyassociating said photoemissive elements with said semiconductive regioncomprises an electrically conductive element.

3. The device of claim 1 in which said photoemissive element is providedon the inner surface of a faceplate member within an evacuated envelope,said sensing member is positioned exteriorly of said envelope andadjacent the outer surface of said faceplate and said means forelectrically associating said photoemissive element with saidsemiconductive regions comprises a plurality of electrical conductivemembers extending through said faceplate.

4. The device of claim 1 in which said semiconductive material issilicon.

5. The device of claim 1 in which said semiconductive material is p-typesilicon and said regions are ntype silicon.

1. An image device comprising an input sensing member comprised of awafer of semiconductive material of a first type of conductivity havingan input and an output surface, a plurality of regions of semiconductivematerial of a second type of conductivity of opposite type conductivityto said first type on the output surface of said wafer and extendinginto said wafer a discrete distance and forming a plurality ofjunctions, said input sensing member exhibiting the property ofgeneration of electron-hole pairs in response to incident radiationdirected onto said input surface, means for reverse biasing saidjunction comprising a photoemissive element and means for electricallyconnecting the photoemissive element with each of said regions and meansfor illuminating said photoemissive elements, an output screenassociateD with said photoemissive elements to generate a light image inresponse to the photoelectrons emitted from said photoemissive elementsstriking said output screen, a first grid positioned adjacent to saidphoto-emissive elements for accelerating the photo-electrons emittedfrom said photoemissive elements and a second grid positioned betweensaid accelerating grid and said output screen for velocity selection ofthe photoelectrons emitted from said photoemissive elements and passingthrough said accelerator grid, said sensing member responsive to saidinput radiations to modify the potential of said photoemissive elements.2. The device of claim 1 in which said means for electricallyassociating said photoemissive elements with said semiconductive regioncomprises an electrically conductive element.
 3. The device of claim 1in which said photoemissive element is provided on the inner surface ofa faceplate member within an evacuated envelope, said sensing member ispositioned exteriorly of said envelope and adjacent the outer surface ofsaid faceplate and said means for electrically associating saidphotoemissive element with said semiconductive regions comprises aplurality of electrical conductive members extending through saidfaceplate.
 4. The device of claim 1 in which said semiconductivematerial is silicon.
 5. The device of claim 1 in which saidsemiconductive material is p-type silicon and said regions are n-typesilicon.